JayMatt, I understand what you are saying, and if the other passengers had said, “excuse me, I think you are on the wrong bus” & politely explained the rules, this would have been perfectly appropriate. At that point Daniel would’ve explained why he sat in the front with his wife & perhaps the other passengers would’ve found a better solution to his dilemma (as he stated, he wanted to sit in the front to reduce his chance of becoming ill and probably wanted his wife next to him so she could help him in case he did become ill). This would have been an appropriate reaction, given that the other passengers were presumably motivated by a desire for tznius.
For those posters who think Daniel was in the wrong here, please explain how the reaction of the other passengers demonstrates tznius? As many have so helpfully pointed out in other threads, tznius is not just about the clothes one wears but also about the way one behaves. And most of us would agree that true tznius brings a kiddush haShem to the world, not chalilah the opposite.